As well known, a refrigeration cycle changes the temperature and pressure in a system and can lead to a phase change of refrigerant. By the latent heat of the evaporation or the latent heat of the condensation, the temperature of the indoor maintains properly or a refrigeration capacity like an ice manufacturing can be accomplished. It categories as an air conditioner like a cooler or a heat pump, a refrigerator and an icing maker according to its use.
A refrigeration cycle for vapor condensation (hereafter referred to “refrigeration cycle”) is a system in which a compressor, a condenser, an expansion valve and an evaporator are connected orderly through a pipe to make a close circuit.
A saturated vapor refrigerant having low pressure and low temperature is compressed into a superheated vapor refrigerant having high pressure and high temperature via the iso-entropy process at the compressor. The superheated vapor refrigerant enters to the condenser so that it heat-exchanges with a circumstance of air under constant pressure to release a heat and it is condensed to saturated liquid having high pressure. The condensed refrigerant passes through the expansion valve and is changed to wet vapor having low pressure and low temperature by throttling. Next, it passes through the condenser and absorbs the latent heat of the evaporation to evaporate. The saturated vapor reenters the compressor and repeats the above cycle.
For example, the air cooler in an air conditioner is an apparatus by which the evaporator is arranged at the indoor, the condenser is arranged at the outdoor, the refrigerant is evaporated by the latent heat of the evaporation which is absorbed from the indoor air.
On the other hand, the heat pump is an apparatus by which the evaporator is arranged at the indoor, the condenser is arranged at the outdoor, and the refrigerant flow direction is changed according to its use by operation of a 4-way valve, thereby carrying through a role change between the condenser and the evaporator. By the heat pump, it heats or cools the indoor using the latent heat of the evaporation that is absorbed by refrigeration evaporation and the latent heat of the condensation that is released by refrigeration liquefaction.
The performance of the refrigeration cycle is expressed by coefficient of performance (COP), which is defined as a ratio of the heat to the work. The heat is quantity of the absorbed heat at an evaporator or quantity of the condensed heat at a condenser, while the work is required when the refrigerant having low pressure and low temperature is compressed into one having high pressure and high temperature by a compressor.
Therefore, the refrigeration effect and a discharge heat capacity, which indicates the heat capacity absorbed when evaporating the refrigerant of 1 kg, must be increased to get superior performance in an air cooler and a heat pump.
However, if the refrigeration effect has increased above the increment along the increase of the compression work, coefficient of performance is rather worse or the consumption of electric power is increased. Coefficient of performance must be improved adequate to the system considering various matters such as a property of refrigerant.
Specially, during heating operation in winter, the refrigerant cannot sufficiently absorb the latent heat of the evaporation due to the low outdoor temperature, causing the evaporation inferiority. The degree of dry saturation of the refrigeration having low pressure is decreased and it leads to the occurrence of the compression inferiority owing to the wet compression. The specific volume of the inflowing refrigerant increases, leads to less generation volume of the condensed heat. It is hard to expect the sufficient heating performance. Moreover, overload is imposed on the compressor to cause the burnout. The consumption of electric power is increased by the large work capacity.
Conventional arts for improving the performance of the above air conditioner are found in Korean patent open-laid Nos. 2002-0070944 and 2002-0042775.
In patent open-laid No. 2002-0070944, the insulated first and second heat recovery apparatuses are installed between a 4-way valve of the heat pump system and an outdoor heat exchanger. Further, a third heat recovery apparatus is installed between a 4-way valve and a compressor. A high-pressure and low-pressure refrigerant pass through the first, second and third heat recovery apparatuses to do heat exchange reciprocally. Thus, the liquid refrigerant having high pressure is super-cooled and the refrigerant having low pressure is compensated for heat.
However, the third heat recovery apparatus is provided between the compressor and the 4-way valve in the heat pump system, the refrigerant having low pressure is flowing into the compressor with excessive heat when in cooling, and that system is very concerned about damage due to the superheating in the compressor. When in heating, the high-pressure refrigerant discharged from the compressor gives the considerable heat to the low-pressure refrigerant at the third heat recovery apparatus, and enters into the indoor heat exchanger. Not enough heating is anticipated.
Moreover, the liquid refrigerant having high pressure passes through an additional super-cooler so as to be super-cooled, which plans to increase the refrigeration effect. However, under the constant pressure, the liquid refrigerant having high pressure is simply dependent on thermal conduction, and it makes the degree of super-cooling to be lowered, and the volume decrease of flash gas of the expanded refrigerant is very slight.
In patent open-laid No. 2002-0042775, a special heat exchanger is installed between an outdoor heat exchanger of the heat pump system and an indoor heat exchanger. Further, using two 4-way valves, the liquid refrigerant having high pressure and the gas refrigerant having low pressure pass through the heat exchangers to make a heat exchange reciprocally. It makes the liquid refrigerant having high pressure super-cooled and also the gas refrigerant having low pressure super-heated, increasing coefficient of performance and decreasing compression work.
However, in this technology, the liquid refrigerant having high pressure does heat conduction at medium temperature under condensed pressure, and it causes a low degree of super-cooling. Since there exists a lot of difference to the evaporation pressure, the volume of flash gas of the evaporated refrigerant is large, and the low absorption volume of the latent heat of the evaporation can be gained. Therefore, the evaporation of heating operation is still inferior in winter.
Further, the quantity of conduction heat is very low comparing to vapor since the liquid refrigerant is simply dependent on heat conduction. More, due to the non-insulation of the heat exchanger, most heat of the liquid refrigerant is released to the air during the heat exchange process, which leads to very low degree of the super-heating of the gas refrigerant having low pressure. Therefore, it is hard to anticipate a decrease of compression load and to accomplish a deduction of consumption of electric power. Specially, no sufficient heating is expected due to lack of the heat capacity when in heating.